It is well known in the art that the introduction of photographically useful compounds, such as photographic couplers, development inhibitors, base, base precursors, fixing agents, i.e., ligand capable of binding silver, silver stabilizing agents and the like, into photographic elements can lead to premature reaction of the photographically useful compound with the other components of the photographic element.
One embodiment of this invention relates to photographic processing and, in particular to a method of fixing employing a fixer sheet that can be laminated to a photographic material to be processed. In conventional photographic processing it is usual to form an image by developing an imagewise exposed silver halide photographic material and then removing the unexposed (and undeveloped) silver halide with a fixer solution. The fixer solution contains a silver halide solvent, typically an alkali metal or ammonium thiosulphate, which forms soluble complexes with the silver halide which then pass into the solution thus leaving the photographic material substantially free of silver halide. The silver salt diffusion transfer process is also well known and provides a black-and-white image by placing an imagewise exposed silver halide material in face-to-face contact with a receiving layer in the presence of a silver halide solvent, a silver halide developing agent and silver precipitating nuclei. In the initial developing phase, a silver image is developed in the silver halide material while, in a second phase, undeveloped silver halide is transported as a soluble complex with the silver halide solvent to the receiving layer where metallic silver is deposited adjacent to the silver precipitating nuclei having been formed by reduction of the solubilised silver halide by developing agent.
In a variation of the above processes it is known to process photographic materials by placing them in face-to-face contact with a receiver sheet in the presence of a developing agent and a silver halide solvent. A recent example of such a process is described in U.S. Pat. No. 4,775,614 in which receiver sheets comprise a water-absorbing polymer layer, silver precipitating nuclei and a silver halide solvent. U.S. Pat. No. 3,179,517 describes a method of fixing black-and-white materials by lamination to a receptor element wherein, inter alia, zinc sulphide is used as a silver ion precipitating agent. The precipitation reaction in this case being a conversion reaction (metathesis). In this reaction the silver halide is converted to silver sulphide and the zinc sulphide to zinc halide.
U.S. Pat. No. 4,480,025 describes the bleaching and fixing of a developed color silver halide photographic material by using a bleach-fix sheet comprising a water-supplying layer, a bleaching agent, a silver halide solvent and a dye mordant. The particular use exemplified is to bleach and fix a color diffusion transfer material so that the retained image is usable. This system operates at an acid pH and contains an oxidizing agent to achieve the bleaching of silver.
Applying the concept of fixing by lamination to a camera speed film material, presents special problems. Due to the practice of using high silver halide levels coupled with partial development of the grains (a technique employed to achieve the best granularity) there are high levels of silver halide to remove. This leads to incomplete removal of silver halide when using previously suggested systems. U.S. Pat. No. 5,478,703 overcomes this deficiency by providing a method of fixing a developed photographic silver halide material comprising at least 2 silver halide layers sensitized to different regions of the spectrum, comprising placing the material in face-to-face contact with a fixer sheet in the presence of a processing solution and a silver halide solvent which forms a solubilised silver halide species from the undeveloped areas of the material, wherein the fixer sheet contains reducing means capable of forming metallic silver therein from the solubilised silver halide. The provision of a means of fixing a photographic film or other material which avoids the need for a separate fixing bath with its associated difficulties of silver recovery or disposal when exhausted is useful. The process can also operate with lower levels of silver halide solvent than conventional fixing baths, and can result in less escape of fixing agent into the environment. The fixer sheet can also conveniently be sent away for recovery and recycling of the silver. An important further advantage of the invention over conventional fixing baths is that it allows products of photographic color processing to be trapped in the receiver sheet and therefore not discharged into the environment. This is particularly valuable for smaller scale photofinishing operations where full-scale pollution control equipment to treat their effluent would be too costly and inconvenient. The silver halide solvent, such as sodium thiosulphate, which is necessary for the process, may be coated in whole or part in the fixing sheet.
Other variations of photographic processing using dry photographic processing elements have been described in the art. In one technique a single processing element is brought into contact with the photosensitive film to carry out photographic development. U.S. Pat. No. 5,440,366 to Reiss and Cocco teaches a photographic processing system and method wherein individual dry photographic processing elements are sequentially wrapped onto a single processing spool.
While there has been interest in carrying out photographic processing of exposed photosensitive film with dry processing elements, the systems and methods described in the prior art have not been entirely satisfactory insofar as providing the desired results. Accordingly, there is a continuing need for novel and improved systems and methods for forming images in exposed photosensitive films using dry photographic processing materials.
Silver halide photothermographic imaging materials, especially "dry silver" compositions, processed with heat and without liquid development have been known in the art for many years. Such materials are a mixture of light insensitive silver salt of an organic acid (e.g., silver behenate), a minor amount of catalytic light sensitive silver halide, and a reducing agent for the silver source. The light sensitive silver halide is in catalytic proximity to the light insensitive silver salt such that the latent image formed by the irradiation of the silver halide serves as a catalyst nucleus for the oxidation-reduction reaction of the organic silver salt with the reducing agent when heated above 80.degree. C. Such media are described in U.S. Pat. Nos. 3,457,075; 3,839,049; and 4,260,677. Toning agents can be incorporated to improve the color of the silver image of photothermographic emulsions as described in U.S. Pat. Nos. 3,846,136; 3,994,732 and 4,021,249. Various methods to produce dye images and multicolor images with photographic color couplers and leuco dyes are well known in the art as represented by U.S. Pat. Nos. 4,022,617; 3,531,286; 3,180,731; 3,761,270; 4,460,681; 4,883,747 and Research Disclosure 29963.
A common problem that exists with these photothermographic systems is the instability of the image following processing. The photoactive silver halide still present in the developed image may continue to catalyze print-out of metallic silver even during room light handling. Thus, there exists a need for stabilization of the unreacted silver halide with the addition of separate post-processing image stabilizers or stabilizer precursors to provide the desired post-processing stability. Most often these are sulfur containing compounds such as mercaptans, thiones, thioethers as described in Research disclosure 17029. U.S. Pat. No. 4,245,033 describes sulfur compounds of the mercapto-type that are development restrainers of photothermographic systems as do U.S. Pat. Nos. 4,837,141 and 4,451,561. Mesoionic 1,2,4-triazolium-3-thiolates as fixing agents and silver halide stabilizers are described in U.S. Pat. No. 4,378,424. Substituted 5-mercapto-1,2,4-triazoles such as 3-amino-5-benzothio-1,2,4-triazole as post-processing stabilizers are described in U.S. Pat. Nos. 4,128,557; 4,137,079; 4,138,265, and Research Disclosures 16977 and 16979.
Some of the problems with these stabilizers include thermal fogging during processing or losses in photographic sensitivity, maximum density or, contrast at stabilizer concentrations in which stabilization of the post-processed image can occur. Stabilizer precursors have blocking or modifying groups that are usually cleaved during processing with heat and/or alkali. This provides the remaining moiety or primary active stabilizer to combine with the photoactive silver halide in the unexposed and undeveloped areas of the photographic material. For example, in the presence of a silver halide precursor in which the sulfur atom is blocked upon processing, the resulting silver mercaptide will be more stable than the silver halide to light, atmospheric and ambient conditions.
Various blocking techniques have been utilized in developing the stabilizer precursors. U.S. Pat. No. 3,615,617 describes acyl blocked photographically useful stabilizers. U.S. Pat. Nos. 3,674,478 and 3,993,661 describe hydroxyarylmethyl blocking groups. Benzylthio releasing groups are described in U.S. Pat. No. 3,698,898. Thiocarbonate blocking groups are described in U.S. Pat. No. 3,791,830, and thioether blocking groups in U.S. Pat. Nos. 4,335,200, 4,416,977, and 4,420,554. Photographically useful stabilizers which are blocked as urea or thiourea derivatives are described in U.S. Pat. No. 4,310,612. Blocked imidomethyl derivatives are described in U.S. Pat. No. 4,350,752, and imide or thioimide derivatives are described in U.S. Pat. No. 4,888,268. Removal of all of these aforementioned blocking groups from the photographically useful stabilizers is accomplished by an increase of pH during alkaline processing conditions of the exposed imaging material.
Other blocking groups which are thermally sensitive have also been utilized. These blocking groups are removed by heating the imaging material during processing. Photographically useful stabilizers blocked as thermally sensitive carbamate derivates are described in U.S. Pat. Nos. 3,844,797 and 4,144,072. These carbamate derivatives presumably regenerate the photographic stabilizer through loss of an isocyanate. Hydroxymethyl blocked photographic reagents which are unblocked through loss of formaldehyde during heating are described in U.S. Pat. No. 4,510,236. Development inhibitor releasing couplers releasing tetrazolylthio moieties are described in U.S. Pat. No. 3,700,457. Substituted benzylthio releasing groups are described in U.S. Pat. No. 4,678,735; and U.S. Pat. Nos. 4,351,896 and 4,404,390 utilize carboxybenzylthio blocking groups for mesoionic 1,2,4-triazolium-3-thiolates stabilizers. Photographic stabilizers which are blocked by a Michael-type addition to the carbon-carbon double bond of either acrylonitrile or alkyl acrylates are described in U.S. Pat. Nos. 4,009,029 and 4,511,644, respectively. Heating of these blocked derivatives causes unblocking by a retro-Michael reaction.
Thus, there has been a continued need for improved post-processing stabilizers that do not fog or desensitize the photographic materials, and stabilizing compounds that release the stabilizing moiety at the appropriate time and do not have any detrimental effects on the photosensitive material or user of said material.
Compounds from which bases are released by heating are referred to as "base precursors". The base precursors are employed in various systems designed so that the bases released by heating can function therein. Examples of such systems include heat-developable photographic materials, heat-sensitive recording materials, anion-polymerizable adhesives, film formation by coating, sealing materials, caulking materials, and the like.
One of the most favorable uses of the base precursors is for various types of image-forming materials for which heat is utilized (e.g., heat-developable photographic materials and heat-sensitive recording materials, etc.). In these materials the over all performance largely depends on the base precursor, because the formation of images takes place by reactions of other chemical species included therein which are activated by the base released by heating. The base precursor must rapidly release the base at a heating temperature as low as possible and be stable to storage conditions at the same time.
Examples of typical base precursors include salts of carboxylic acids and organic bases as described in U.S. Pat. No. 3,493,374 (triazine compounds and carboxylic acids), British Patent 998,949 (trichloroacetic acid salts), U.S. Pat. No. 4,060,420 (sulfonylacetic acid salts), JP-A-59-168441 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") (sulfonylacetic acid salts), JP-A-59-180537 (propiolic acid salts), JP-A-60-237443 (phenylsulfonylacetic acid salts substituted by a sulfonyl group), and JP-A-61-51139 (sulfonylacetic acid salts). Other base precursors which have heretofore been known include ureas as described in U.S. Pat. No. 2,732,299 and Belgian Pat. No. 625,554, ammonium salts of urea or urea and weak acids as described in Japanese Patent Publication No. 1699/65, hexamethylenetetramine and semicarbazide as described in U.S. Pat. No. 3,157,503, dicyandiamide derivatives as described in U.S. Pat. No. 3,271,155, N-sulfonylureas as described in U.S. Pat. No. 3,420,665, and amineimides as described in Research Disclosure, RD No. 15776 (1977). The use of these salts as the base precursors stems from the fact that decarboxylation of the carboxylic acids by heating results in the release of the organic bases. However, these precursors have been insufficient in compatibility of rapidity of the release of the bases on heat treatment (activity) with stability on storage (storability).
The most useful base precursors are salts of a carboxylic acid and an organic base. Examples of useful carboxylic acid are trichloroacetic acid and trifluoroacetic acid, and examples of useful base are guanidine, piperidine, morpholine, p-toluidine, and 2-picoline. Particularly useful base precursor is guanidine trichloroacetate as described in U.S. Pat. No. 3,220,846. Further, aldoneamides described in Japanese Patent Application (OPI) No. 22625/75 (the term "OPI" as used herein means a "published unexamined Japanese patent application") decompose at high temperatures to release a base, and are preferably used.
Of the base precursors described above, water-soluble base precursors, however, have a disadvantage such that they are easily changeable on reacting with other components contained in coating materials. Furthermore, since those water-soluble base precursors are added in the form of an aqueous solution, those are uniformly present in the coating and are readily affected by air or moisture. Hence, the water-soluble base precursors are decomposed under the action of air or moisture to change photographic characteristics of the light-sensitive material, thereby deteriorating the storage stability of the light-sensitive material.
Water-insoluble base precursors have heretofore been used in the manner such that these are first dissolved in an organic solvent which is compatible with water, such as methanol, ethanol, acetone, or dimethylformamide, and then the resulting solution is added to an emulsion layer and/or its adjacent layer of the light-sensitive material. This is an industrially convenient method to introduce a water-insoluble additive into the light-sensitive material. In the method, however, the amount of the solvent which can be introduced into the light-sensitive material is limited. No serious problem arises when the amount of the additive added is small but in the case of the base precursor which must be added in a large amount, the amount of organic solvent which is required to dissolve therein the base precursor often exceeds the upper limit. Furthermore, many base precursors are sparingly soluble in such organic solvent which is compatible with water and those are difficult to add to the light-sensitive material.
There therefore exists the need for base precursors that have high mobility in photographic coatings, yet will remain immobile during raw stock keeping and not interact with other components or air. The base precursors of the present invention, ionically bound to an ion exchange matrix, are immobile. The compounds are tightly bound to the resin and do not wander through a coating. This includes not only compounds that have limited aqueous solubility, but also compounds that are highly water soluble.